Fibre reinforced plastic composites are used in a variety of technical products such as Cars, Aeroplanes, Wind Turbine Blades, Storage tanks, etc. In many cases, the fibre parts are placed in a mould. The mould is closed by a second mould part or a plastic liner is placed over the mould, and vacuum is applied to the fibre filled hollow structure. A liquid resin is then infused from a mixing facility. The mixed resin fills out the space between fibres, and finally cures. In this way, a rigid reinforced composite structure is made.
The resin flows into the mould cavity through inlet holes distributed over the mould surface. A typical example of this process is the Vacuum Assisted Resin Transfer Moulding, called VARTM.
Resin flow channels may be used to enable a fast flow to certain areas of the mould system. Often a special resin flow medium is placed between the vacuum foil and the glass fibres to be wetted by the resin. When the resin is sucked into the mould cavity, it flows fast through the flow medium, whereas the glass material is denser and exhibits a higher resistance to the resin flow. Partly forced by vacuum and partly by capillary forces, the resin is further distributed into the fibre material. As the resin flows over an area, the foremost area of the resin in movement is called the resin flow front. As the resin travels through the flow medium, the static vacuum declines behind the flow front. The highest vacuum is found in the air filled space in front of the flow front. Therefore, the resin flows fast through the flow medium, passing over the fibre material to be wetted.
It would be desirable to have a slower movement of the flow front, and a higher flow of resin perpendicular to the surface, from the flow medium and into the laminate. A fibre layout with unidirectional fibres, such as a non-woven roving laminate, especially with high fibre content, will have a much reduced resin flow, due to the compact build-up of fibres.
To enable a correct wetting of all fibres inside the mould, a complex layout of resin channels and flow sheets are placed in the mould. In thick sandwich constructions, the core panels, such as balsa wood panels, are often equipped with cut channels to enable faster flow of resin along the core material surface. This is done to enhance the penetration of resin from both sides of a laminate, to get the fastest possible wetting of the total fibre stack. However, the extra resin channels take up extra amounts of resin, which makes the parts heavier and more expensive. For laminates with high fibre content, such as unidirectional roving laminates, it is necessary to include layers of open fabrics that enable a better resin flow. The incorporation of open fabrics for better flow yields laminates with reduced modulus of elasticity (E-modulus) and heavier weight due to the higher resin content.